Transcranial anodal stimulation (tDCS) improves manual dexterity in healthy old adults. The underlying changes in finger force behavior for this improved dexterity have not been reported. Here, we investigated the effects of tDCS (20-min) over primary motor cortex (M1) combined with repeated practice on the Grooved pegboard test (tDCS+MP) on the fingertip forces applied to an object during grasp and manipulation. Eight right-handed able-bodied individuals (60-85 years) participated in a sham-controlled, single-blinded study. Each participant received anodal and sham intervention in two sessions at least 5-day apart. Before and after intervention, they performed a ‘key-slot’ task that required inserting a slot on an object onto a stationary bar, an isometric force production task using a pinch grip, and the Grooved pegboard test. Anodal relative to sham tDCS+MP allowed participants to better retain the improved performance on the pegboard test. For the isometric task, anodal tDCS+MP significantly increased the variability of force compared to sham tDCS+MP. More importantly, the improved retention of performance post-anodal tDCS correlated with the reduction in force angle variability on the key-slot task, but not with the change in force variability on the isometric task. Our findings suggest that anodal tDCS+MP facilitated retention of learning on a skillful manual task in healthy old adults, consistent with the role of M1 in retention of learning versus skill acquisition. Furthermore, improved force steadiness is one of the potential mechanisms through which short-term anodal tDCS during motor training yields improved performance on a functional task.
Listed In: Biomechanics, Neuroscience